A little confusing perhaps, but you're right on 2 fronts, 1) what stats you look at, and 2) the economy
The latter definately has caused a decline of illegal Mexican immigrants, though they still pour in. What is pouring in, in record #'s are all those immigrants that Obama pledged could stay from other countries, if they were supposedly running away from persecution. Those #'s are soaring...and made worse in that the Mexican government is literally helping them cross their country.
So yea, Illegal Mexican Immigration is down....a little. Illegal Everything-else immigration is shooting up